1. Technical Field
The present invention relates to a real time clock and a method for recording data in a real time clock.
2. Related Art
A real time clock is known as an apparatus for recording information indicating the time-of-day of occurrence of an event in a built-in memory and is disclosed, for example, in JP-A-2003-132470. The real time clock disclosed in JP-A-2003-132470 includes an oscillator circuit, a frequency dividing circuit, a timing circuit, an interface circuit, an operation control circuit, an event detection circuit, and an event storage memory. In the real time clock thus configured, the event storage memory stores data including information indicating the time of day of occurrence of an event detected by the event detection circuit and information specific to the event, as one piece of event data.
By using the real time clock configured as described above, a user is allowed to identify an event that has occurred at a recorded time-of-day, on the basis of event information stored in the event storage memory. While JP-A-2003-132470 discloses that the real time clock includes, as power supply systems, a so-called “main power supply” that provides power from a wall outlet and a backup power supply that provides power from a primary or secondary cell, it has no countermeasures against an unexpected situation such as a voltage reduction or an oscillation stop. Therefore, if erroneous data is written into the event storage memory due to a voltage reduction or the like, the real time clock cannot make a determination about the correctness of the stored data cannot be determined. As a result, the reliability of stored specific event data is low.